OptionalcallSIP URI of the destination endpoint. Both sip: (unencrypted) and sips: (TLS-encrypted) schemes are supported.
OptionaltransportTransport protocol to use for the SIP signalling channel. If omitted, the platform selects a default based on the URI scheme: UDP for sip: and TLS for sips:. Setting this explicitly overrides that default — for example, to force TCP for a sip: URI or to use TLS without switching to the sips: scheme.
Custom SIP headers to be sent in the call setup.